This invention relates to intraluminal stent implants for maintaining support of a body lumen. It comprises an improvement and alternate design to stents which are generally cylindrical in shape and have a plurality of metal elements joined to permit flexing of the stent along the longitudinal axis allowing it to conform to the curves of the inner wall of the targeted lumen.
An important use of metal stents is found in situations where part of the vessel wall or stenotic plaque blocks or occludes blood flow in the vessel. Normally a balloon catheter is utilized in a percutaneous transluminal coronary angioplasty (PTCA) procedure to enlarge the occluded portion of the vessel. However, the dilation of the occlusion can form flaps, fissures and dissections which threaten re-closure of the dilated vessel or even perforations in the vessel wall. Implantation of stents can provide support for such problems and prevent reclosure of the vessel or provide patch repair for a perforated vessel. The stent overcomes the natural tenancy of the vessel walls of some patients to collapse, thereby maintaining a more normal flow of blood through that vessel than would be possible if the stent were not in place.
An example of prior developed metal stents has been described in the article of Stignart, et al. titled "Intravascular Stents To prevent Occlusion and Restenosis after Transluminal Angioplasty", published in the New England Journal of Medicine, Vol. 316, No. 12, Mar. 19, 1981, pages 701-706. This stent is the form of a "Chinese finger handcuff" metallic mesh which can be expanded and compressed in diameter. The stent is made by cutting desired lengths from an elongated tube of metal mesh and, accordingly, has the disadvantage that metal prongs from the cutting process remain at the longitudinal ends thereof. The inherent rigidity of the metal used to form the stent together with these terminal prongs make navigation of the blood vessels to the locus of the lesion difficult as well as risky from the standpoint of injury to healthy tissue along the passage to the target vessel. When the stent is permanently placed in a vessel, the continuous stress from the flow of the fluid within the vessel could cause the prongs to damage the vessel walls adjacent to the lesion.
Another type of metal stent involves a tube of stainless wire braid. During insertion, the tube is positioned along a delivery device, such as a catheter, in extended form, making the tube diameter as small as possible. When the stent is positioned across the lesion, it is expanded, causing the length of the tube to contract and the diameter to expand. Depending on the materials used in construction of the stent, the tube maintains the new shape either through mechanical force or otherwise. The alteration in the length is undesirable due to the deformation of the stent, the longitudinal abrasion on the inner wall and the unpredictable coverage when fully in place.
An additional form of metal stent is a heat expandable device using Nitinol or a tin-coated, heat expandable coil. The stent is delivered to the affected area on a catheter capable of receiving heated fluids. Once properly situated, heated saline is passed through the portion of the catheter on which the stent is located, causing the stent to expand. Numerous difficulties have been encountered with this device, including difficulty in obtaining reliable expansion, and difficulties in maintaining the stent in its expanded state.
A popular metal stent is the Palmaz stent. It involves a stainless steel cylinder having a number of slits in its circumference, resulting in a mesh when expanded. The stainless steel cylinder is delivered to the affected area by means of a balloon catheter, and is then expanded to the proper size.
Stents can be deployed in a body lumen by means appropriate to their design. One such method would be to fit the collapsed stent over an inflatable element of a balloon catheter and expand the balloon to force the stent into contact with the body lumen. As the balloon is inflated, the problem material in the vessel is compressed in a direction generally perpendicular to the wall of the vessel which, consequently, dilates the vessel to facilitate blood flow therethrough. Radial expansion of the coronary artery occurs in several different dimensions and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon and hardened deposits are cracked and split to enlarge the lumen. It is desirable to have the stent radially expand in an uniform manner.
Alternatively, the stent may be mounted onto a catheter which holds the stent as it is delivered through the body lumen and then releases the stent and allows it to expand into contact with the body lumen. This deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the catheter.
It is desirable to provide a stent that has sufficient structural integrity to be placed within a vessel at the site of a stenotic lesion, or the like, to support the vessel wall against collapse and yet is flexible and compliant enough for safe and effective delivery to the site of an obstruction. It would also be desirable to provide a stent which is soft and compliant enough to avoid arterial rupture or aneurysm formation at the ends of the stent even when exposed to continuous stresses from the beating heart during chronic implantation.
Significant difficulties have been encountered with all prior art stents. Each has its percentage of thrombosis, restenosis and tissue in-growth, as well as varying degrees of difficulty in deployment. Another difficulty with at least some of prior art stents is that they do not readily conform to the vessel shape. The relatively long length of some prior art stents has made it difficult to treat curved vessels, and has also effectively prevented successful implantation of multiple such stents. Stents illustrated in the prior art tend to go through plastic deformation during expansion and as a result the expansion device does not expand uniformly to the shape of the targeted lumen. Thus there is a need for an effective stent that maintains an open vessel, is easily delivered to the affected area, one that is easily expanded to a desired size, and maintains that size, easily conforms to the shape of the effected vessel, and is easily used in multiples to treat curved vessels and varying lengths of lesions. The stent should not alter in length during expansion or incorporate plastic deformation during such uniform expansion.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn.1.56(a) exists.